1. Technical Field
The present invention relates to a bonding apparatus and more particularly to a bonding apparatus that includes a moving mechanism which moves a bonding section that performs bonding work into arbitrary positions.
2. Description of the Related Art
A wire bonder connects a plurality of bonding pads disposed on a die of semiconductor chip or the like, with bonding leads disposed on a circuit board or the like by means of a fine gold wire or the like. In order to achieve correct positioning and bonding of such a gold wire or the like in specified positions on such bonding pads and bonding leads, a wire bonder needs to have a mechanism that moves a bonding head, which is mounted with a bonding tool (that allows a gold wire to pass through and holds the gold wire) and a positioning camera, to arbitrary positions is required.
FIG. 9 is a top view of the moving mechanism of the bonding head 20 in a conventional wire bonder 10 disclosed in Japanese Patent Application Laid-Open (Kokai) No. 2002-329772.
The mechanism used in this prior art is known as a so-called XY table mechanism; and in this mechanism, an X table 16 and Y table 18 are provided on top of a table holder 14 disposed on the upper surface of the stand 12 of the wire bonder 10, and the bonding head 20 is provided on the Y table 18. A bonding tool 22 (which has at the tip end a capillary through which a gold wire is passed and in which the gold wire is held) and a position detection camera 24 are mounted on the bonding head 20. A circuit board conveying path 50 is disposed on the stand 12, and circuit boards are conveyed to a bonding work region 52 that is located substantially directly beneath the bonding tool 22.
Accordingly, by way of moving the bonding head 20 to an arbitrary position in the XY plane by moving the X table 16 in the X direction and by moving the Y table 18 in the Y direction over the surface of the X table 16, the position to be bonded on a circuit board is detected using the position detection camera 24, and the bonding tool 22 is moved into the desired position based upon this detection. The bonding tool is then moved in the Z direction by means of a Z direction moving mechanism (not shown in FIG. 9) so that bonding is performed.
The X table 16 is driven by an X direction linear motor 30 and is guided by a linear guide (not shown in FIG. 9) so that the X table 16 is moved in the X direction over the surface of the table holder 14. More specifically, the X direction linear motor 30 comprises a driving portion 32, which generates a driving magnetic field in a direction perpendicular to the coil, and a movable coil 34, which receives a thrust in the X direction from the driving magnetic field when a coil current is caused to flow. The movable coil 34 is connected to the X table 16 via an arm 36. The Y table 18 is driven by a Y direction linear motor 40 and is guided by a linear guide (not shown in FIG. 9) so that the Y table 18 is moved in the Y direction over the surface of the X table 16. The Y direction linear motor 40 also comprises a driving portion 42, which generates a driving magnetic filed in a direction perpendicular to the XY plane, and a movable coil 44, which receives a thrust in the Y direction from the driving magnetic field as a result of the X direction component current that is generated when a coil current is caused to flow. The movable coil 44 is connected to the Y table 18 via an arm 46.
As seen from the above, the bonding head is moved to an arbitrary position by using such an XY table mechanism. However, since this mechanism is driven by applying a thrust generate by the cooperative action of the movable coils of linear motors and driving magnetic fields directly to the bonding head, there are limits to the increase in speed that is possible (as will be described below).
Where F is the thrust of the motor, m is the mass of the movable part such as the movable coil, etc., in the motor, and M is the mass of the bonding head and table, etc., that are driven, then the acceleration α is indicated by α=F/(M+m). The acceleration increases to some extent by reducing M as far as possible; however, the limit in this case is determined by F/m. If the size of the movable part of the motor increases, e.g., if the number of turns of the movable coil is increased, the thrust F increases. At the same time, however, the mass of the movable part also increases. Accordingly, if an attempt is made to use a motor with a higher power, F/m, which is the limit of the acceleration a, is still hit as an upper limit, and there are limits to the increase in speed.